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Harrison FMOD inline HP rca filters, or ???
I'm looking at designing/building a line-level HP filter in a two-way bi-amped set-up (using a broad ranger), ~190Hz. I've been a bit confused on building my own, as needing and not seeing the input impedance of my Legacy Powerbloc4. I did see that other Legacy amps have an input impedance of 38K, but not my specific amp. I'm thinking it as a good idea to place a HP line level as some protection for the broad ranger (turn on pops, etc.), in addition to the HP slope. I've seen that 1st order with caps post-amp as HP with broad-rangers end up being pretty much worthless due to impedance issues in the lower end, and in any event massively large. And, I'm a bit uncertain as some examples exclude the r from RC using just the input impedance of the amp, others discuss r being the parallel of an r with the input impedance of the amp? I'm coming up with 0.022uf in series cap but ???
So, any specific values / design (i.e. RC and/or C with r being the amp) and/or comments on the Harrison filters would be greatly appreciated. I've experimented with a cap in-line, but it looks to draw down the full range of the broad-ranger more so than rolling off at a frequency?
Edit: the top line is the broad-ranger no HP, the next two are active HP (190Hz, 240Hz) the lower are passive 0.047 and 0.022 (cap in series only, no add’l resistor).
Comments
What's the slope of the active HP? I would assume passive components will act the same as they do in a crossover, so you only have a 6dB slope with the cap - maybe less by the look of it? I would probably go without any filters and just make sure that amp is the last one turned on and the first one turned off. They used to make AC controllers that did that - I'm thinking it was an Adcom or Rotel.
Actives are 1st order. I’m thinking the passive calculations, based on (apparently wrong) assumption of amp input capacitance is way off - to small. Maybe I need to add parallel resistor - but not sure what value.